Conventionally, electric switches of this type consisted of a number of two-pole switches having independent contact units which are adapted for individual actuation for achieving the on-off control, the speed control, the reversal control of the rotational direction, and the quick stop of the motor for such a power tool. For instance, a rotary switch having a rotatable knob for switching over the polarity of the electric current supplied to the motor rotor is used for reversing the rotational direction of the motor in addition to the main control switch for controlling the on-off of the motor and, in many cases, the rotational speed of the motor.
However, the use of a large number of contact units tended to increase the number of component parts for the switch unit and made its structure highly complex, and this factor has been detrimental to the simplification of the assembly process and the reduction of the overall size and the cost of the switch structure.